1. Field of the Invention
The present invention relates to a liquid crystal display, and particularly relates to a multiple view liquid crystal display capable of displaying a plurality of images in respectively different directions.
2. Description of the Background Art
Taking advantage of merits of consuming low power and being compact and lightweight, a liquid crystal display has been applied to any display such as monitors of a personal computer (PC), mobile information terminal equipment and the like, and a television receiver. The liquid crystal display is a device which is provided with a plurality of pixels arranged in matrix form and performs optical modulation on each pixel, to display an image. As a representative example of the liquid crystal display, there is widely known an active matrix-type display using a thin film transistor (TFT) as a switching element to supply an image signal to each pixel.
In recent years, there has been developed a multiple view liquid crystal display (multiple screen liquid crystal display) capable of displaying a plurality of images with view angles in respectively different directions by means of one liquid crystal display panel (liquid crystal panel). For example, Japanese Patent Application Laid-Open No. 2007-264082, Japanese Patent Application Laid-Open No. 2008-064917 and PCT International Publication No. WO2007/001071 each disclose a parallax barrier-system multiple view liquid crystal display, especially a dual view liquid crystal display (two-screen liquid crystal display) where an image displayed when viewed from the right side to the front of a screen and an image displayed when viewed from the left side thereto are different.
The parallax barrier-system multiple view liquid crystal display has a structure including a liquid crystal panel where pixels to display a plurality of images are mixed and arrayed in accordance with a predetermined rule, and a light blocking layer called a parallax barrier disposed on the front side (viewed side) of the panel. The parallax barrier is arranged so as to block light travelling in a specific direction from each pixel of the liquid crystal panel. Thereby, light from the liquid crystal panel is separated into a plurality of directions, and a plurality of images displayed on the display panel are displayed in respectively different directions.
The parallax barrier-system multiple view liquid crystal display has a problem of a “crosstalk”, by which part of an image that should be displayed in the other direction is leaked and observed in an image displayed in one direction.
For example, when the crosstalk occurs in a parallax barrier-system dual view liquid crystal display that displays two images separately on the right and left, an image (image for left) that should be displayed when the screen is viewed from the left to the front and an image (image for right) that should be displayed when viewed from the right to the front are viewed as overlapping each other. This crosstalk occurs when view angle ranges (visual field ranges) of the respective images overlap, and tends to occur in the vicinity of a boundary of the visual field ranges of the respective images. That is, in the dual view liquid crystal display, the crosstalk tends to occur when the screen is viewed from the front as the boundary between the visual field range of the image for right and the visual field range of the image for left. Especially when an image with a large amount of black is displayed, even a slight leak from the other image tends to be viewed, thus having a large affect on image quality.
The crosstalk is considered to be mainly caused by, other than the design problem of the multiple view liquid crystal display, a light diffraction phenomenon at the opening in the parallax barrier, a light scattering phenomenon inside the liquid crystal panel, and the like.
Generally, the liquid crystal panel has a structure including a first substrate disposed with a pixel electrode, and a switching element, a signal line and the like which supply a pixel signal to the electrode. The structure includes a second substrate disposed with a black matrix and a color filter (CF) which define an area of each pixel. The structure includes a liquid crystal sandwiched between the first and second substrates. In the parallax barrier-system dual view liquid crystal display, the black matrix to define pixel areas is formed on the front surface of the second substrate which is opposed to the first substrate, and the parallax barrier is formed on the opposite surface thereto (on the viewed side). Hence there exists a gap having a predetermined thickness between the parallax barrier and the black matrix. For example, when the parallax barrier is arranged on the black matrix with a translucent substrate such as a glass substrate constituting the second substrate interposed therebetween, a thickness of this translucent substrate corresponds to the gap. A size of this gap serves as an element to decide a direction and a width of a visual field range of each of a plurality of simultaneously displayed images, along with a size of an opening in the parallax barrier, a pitch of pixels, and the like.
In the parallax barrier-system multiple view liquid crystal display, there occurs a phenomenon called a “reverse view”, by which an image that should be displayed in the reverse direction is viewed when the screen is viewed from the direction greatly off the front, due to the existence of the gap between the parallax barrier and the black matrix. For example, when an observer moves from the front of the screen to the right with respect to the dual view liquid crystal display, there is a range from which the image for right is first viewed and the image for left is then viewed as the observer keeps moving to the right. This is attributable to that another pixel, which is a pixel next to a pixel that should essentially be viewed, is undesirably viewed through the opening in the parallax barrier (a detail will be described later).
That is, in the parallax barrier-system dual view liquid crystal display, the visual field range of the image for left due to the reverse view phenomenon exists outside the visual field range of the image for right, and the visual field range of the image for right due to the reverse view phenomenon exists outside the visual field range of the image for left. For this reason, the crosstalk between the image for right and the image for left occurs not only in the vicinity of the front of the screen, but in practice tends to occur in the vicinity of the outer end of the visual field range of each of the image for right and the image for left. Hereinafter, the crosstalk that occurs in the vicinity of the front of the screen is referred to as a “front crosstalk”, and the crosstalk that occurs in the vicinity of the outer end of each visual field range of each image is referred to as a “reverse view crosstalk”.
The front crosstalk and the reverse view crosstalk are problematical not only in the dual view liquid crystal display, but also in an arbitrary multiple view liquid crystal display having a parallax barrier system.
Each of foregoing Japanese Patent Application Laid-Open No. 2007-264082, Japanese Patent Application Laid-Open No. 2008-064917 and PCT International Publication No. WO2007/001071 mainly discloses a method for preventing the front crosstalk in the dual view liquid crystal display, but does not sufficiently discloses a measure against the reverse view crosstalk. For example, Japanese Patent Application Laid-Open No. 2007-264082 does not refer to the problem of the reverse view crosstalk at all. Japanese Patent Application Laid-Open No. 2008-064917 refers to occurrence of the reverse view crosstalk, but does not particularly take an effective measure thereagainst. PCT International Publication No. WO2007/001071 shows that in a vehicle-mounted dual view liquid crystal display, a range where the reverse view phenomenon occurs is a range which can hardly be viewed from a driver seat and a passenger seat (outside from the front by not less than 45°), but does not refer to a method for substantially preventing the reverse view crosstalk.
On the condition that an angle at which the reverse view phenomenon occurs is set extremely outside by application of the technique of PCT International Publication No. WO2007/001071, the reverse view crosstalk may be prevented, but for implementation thereof, it is necessary to make the gap between the parallax barrier and the black matrix smaller and make the pixel pitch larger. However, since the pixel pitch recently tends to decrease with improvement in definition of the display, it is in practice necessary to make the gap between the parallax barrier and the black matrix extremely small. For example when the gap is formed by the translucent substrate constituting the second substrate, the translucent substrate needs to be made extremely thin, but this is difficult to implement since there is a physical limit for this.